In recent years, as a method of producing a multilayer printed wiring board, a production technique using a build-up method in which resin insulating layers and conductor layers are alternately stacked on a conductor layer of an inner-layer circuit board has been drawing attention. For example, there have been proposed methods of producing a multilayer printed wiring board in which, after coating and heat-curing an epoxy resin composition on an inner-layer circuit board having a circuit formed thereon, the resulting surface is treated with a roughening agent to form an irregularly roughened surface and a conductor layer is subsequently formed by plating (see Patent Documents 1 and 2). Further, there has also been proposed a method of producing a multilayer printed wiring board in which an adhesive sheet of an epoxy resin composition is laminated and heat-cured on an inner-layer circuit board having a circuit formed thereon, the resulting surface is treated with a roughening agent to form an irregularly roughened surface and a conductor layer is subsequently formed by plating (see Patent Document 3).
Describing one example of a method of forming a layered structure of a multilayer printed wiring board by a conventional build-up method while referring to FIG. 1, first, an outer conductor pattern 8 is formed on both sides of a laminated substrate X comprising an inner conductor pattern 3 and a resin insulating layer 4 that are formed on both sides of an insulating substrate 1 in advance, and a resin insulating layer 9 is then formed on each outer conductor pattern 8 by arranging an insulating resin composition such as an epoxy resin composition thereon by coating or the like and subsequently heat-curing the resin composition. Next, after appropriately forming a through-hole 21 and the like, a conductor layer is formed on the surface of each resin insulating layer 9 by electroless plating or the like and a prescribed circuit pattern is formed on the conductor layer in accordance with a conventional method, thereby an outermost conductor pattern 10 can be formed.
In a multilayer printed wiring boards, as a method of forming a resin insulating layer between layers (hereinafter, referred to as “interlayer insulating layer”), as described in Patent Document 3, a method in which a resin insulating layer is formed by laminating and then heat-curing a dry film that comprises a resin layer obtained by coating and drying a thermosetting resin composition such as an epoxy resin composition on a film is employed.